Electrolytic refining of metallic zinc-bearing materials.



"UNITED STATES PA ENT onnron.

.OHARLES H. ALDRICH AND JOHN K. BRYAN, F BALTIMORE, MARYLAND, ASSIGNORS TO (I ELECTROLYTIC ZINC COMPANY, INC., YORK.

No Drawing.

To all whom it may concern Be it lmown that we, CHARLES H. ALDRLCH and JOHN K. BRYAN, both'citizens of'the United States; residing at Baltimore, in the.

State of Maryland, have invented certain new and useful Improvements in Electrolytic Refining of Metallic'Zinc-Bearing Materials, of whichthe following is a speci cation.

This invention relates to a method of refiningmetallic zinc-bearing materials by the electrolytic process, and has for its object to obtain a coherent reguline deposit of zinc on the cathode, free from impurity, sponge or moss. These difficulties incident to the deposition of pure zinc are well recognized and various explanations have been offered. One undoubted fact is that since zinc is more electro-positive even than nickel, all the .heavy metals must be removed before its deposition is attempted. It has been stated,

that the sponge was produced chiefly when a weak solution, or a low Current-density was used, and that hydrogen was usually evolved simultaneously. The cause. of the spongy deposit is variously explained, some authorities ascribing it to the existence of a compound of. zinc and hydrogen, while others trace it to the presence of oxid, produced, for

example, either by the use of a solution con:

taining a trace of basic salt of zinc, or by.

the presence of a more electro-negative metal,

which, being co-deposited, sets up local action at the expense of the zinc.

In the present process accordingly we have had it in view to secure so far as possi-' well known or preferred practice so as to avoid segregation within the electrolyte, that Specification of Letters Patent. Application filed July 26, 1916. Serial No. 111,350.

the cathode, cathode zinc.

the aci helps to ELECTROLYTIC REFIHING on METALLIC ZINC-BEARING MATERIALS.

'Patented Apr. s, 1919.

is, to maintain the homogeneity of the electrolyte. c T

' It has been common practice-heretofore'in the electrolytic refining of zinc to employ a neutral or basic sulfate solution, which, 'as

indicated above,'probably gave rise to someof the various difficulties encountered, such as'mossy deposit, non-adherent deposit upon andthe production of impure Accordingly, as one of the improvements which we have devised, we employ'a slightly acid electrolyte, and have found that'the beststrength of acid to'maintam 1n the electrolyte is about .1 to about .5

per cent..of free sulfuric acid, this 65 of one acidity tion of ously, or the electrolytic circuit, be regenerated in this being maintained either by the addiby placing, insoluble anode tanks in so that the acidmay manner with the. ac-

companying deposit of metallic zinc, the resultant electrolyte being returned to the regular circuit, thus furnishing the acid required. The limits for the acid as given more acid might not be detrimental, and it is possible that less than'.1 of one percent. might be used to good effect in connection with a rapid circulation of the electrolyte,

because rapid circulation would probably give smoother deposit and asmooth deposit would a slightly acid electrolyte is not detrimental-on the contrary, it is beneficial as it produce a reguline deposit on the cathode, cathode with the zinc. A possible explanasulfuric acid at'intervals or continu-' robably not dissolve soquickly in (ii We have found that iron in such,

and does not precipitate on the OF NEW YORK, N. Y., A CORPORATION OF v above are believed to, be about the best, but

tion of this action is that some of the ironj may act as an oxidizing agent, to prevent the formation of zinc hydrate, to whichsome authorities have attributed the formation'of' zinc sponge. At any rate, we have found that we can allow the iron to reach as high as one gram-per liter with good results as to the character of the cathode deposit.

Should the iron in solution go above a point p which may be determined upon as the dam ger point, it can be removed by any of the well known methods, such as precipitation with zinc oxid in a neutral" solution. The temperature of the electrolyte we prefer to keep at about 4i0 C. or lower, as this-seems to be the optimum in the light of-our experiments thus far, though a somewhat higher temperature might be employed 7 We have found that cadmium, which is one of theimpurities that gives particular trouble, :does not go into'solution in the electrolyte,"so long as the slimeis kept in contactjwith the excess zinc remaining in the anode, this being due to the fact that cadmium is more electro-negative than zinc. On this account, and for other'reasons which will be obvious, we propose to surround the anode with a ba or similar envelop, .which may be made 0 duck, canvas'or. the like, ,which bag preferably fits the anode snugly throughout the whole operation. This anode envelop of cours'e prevents the impurities from the anode, which remain as slime, from mechanically contaminating the cathode deposit; and it cuts down the percentage of slime produced, because the slime, being always in contact with the anode, continues to act as part of the anode, and the zinc 0011- tent of the slime continues to dissolve, due

to electrolytic action. It also insures that the cadmium content of this slime remains in close contact with the excess zinc remainand consequently does not ing in the anode, 7 go into solution. Furthermore, this closefitting envelop serves to maintain the im tegrity of the anode, thatis, prevents the in the former practice, tom of the cell and consequently be afl'ected by electrolysis very little, ifat all. a The form of bag which we prefer to employ, and the 'means'for insuring that the bag shall at all times snugly-fit the anode, notwithstanding the by lectrolys'is, is described in an application 1916, in the name of Heber M. Stuart.

Should, by anyaccident, cadmium go into solution, it can be removed by circulating the electrolyte through a anode tanks for a few hours, the time being v dependent on the amount of cadmium prescut and the current density; since cadmium, being more electro-negative than zinc, will be removed with a portion of the zinc, the resulting electrolyte may then be run back to the main circuit, free from cadmium.

We have also foundthat it is racticable, where a series of electrolytic tanl s'are used,

in WhlCl'L'tllB usu'al zinc sulfate electrolytes arefiowing continuously from No. 1 tank through the series to No. X tank, using either soluble or insoluble anodes, the impurities, such as cadmium, and particularly this metal, which is detrimental to high grade dropping off of flakes from the anode, which, would fall to the botgradual disintegration of the anode" series of insoluble for Patent, Serial No. 111367, filed July 26th,

. form,

of cadmium or the like by means" secure pure cathode zinc as zinc in the first tank of the series, the exact numberv necessary for the removal of this cadmium,or other metal more electro-negati-ve than zinc, depending on various factors, such as the currentdensity and the amount of the undesired metal in solution. For instance, if the series included twenty tanks we might take out the impure cathode zinc, including the i co-deposited undesirable metals, from the first four or five tanks, the cathode zinc in the remaining tanks being free from cadmium or other undesired 1 metals, or at least below the limits allowed for high grade zinc specifications. And this may be .done whether soluble orinsoluble anodes are employed, so that while, as before stated, we aim to prevent th co-deposition r of the close-fitting envelop for the anode, etc., the? methodlast above described enables us to .85

the result of the operationcf the cyclic process even though the bag be not used; it being understood that in former practice the impure cathode Zinc from the-first of a series of tanks was invariably removed and mixed with the purer zinc from the later tanks in the series, the resulting mixture being of course contaminated.

Inasmuch as many changes'could be made in the above construction, and manyappar- 'ently widely difierent embodiments of our invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description tended to cover all the generic and specific 115 v features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said tofall therebetween. I

We claim: ,1. As a: step in the electrolytic separation of metallic zinc-bearing materials in anode form, keeping the cadmium content of such materials out of solution .during the-electrolsis. y 2. As a step in the electrolytic separation of metallic zinc-bearing materials in anode form, keeping the cadmium content of the electrolytically disintegrated anode in contact with an excess of'zinc during the electrolysis to prevent the going into solution or the cadmium.

3. As a step in the electrolytic separation of metallic zinc-bearingn'materials in anode keeping the cadmium content of the electrolytically disintegrated anode in conanode during the electrolysis toprevent the going into solution of the cadmium. 65 p t may e removed with the cathode 4:. As a step in the electrolytic separation of metallic zinc-bearing materials including 7 a metal moreelectro-negative than zinc and in anode form, keeping the said more electro-negative-metal content of the electrolytically disintegrated anode in contactwith an excess of zinc-during the electrolysis to prevent the going into solution of said more electro-negative metal.

.5. As a step in the electrolytic separation of metallic zinc-bearing materials-including a metal more electro-negative than zinc and in anode form, keeping the said more electro-negative metal content of the electrolytically disintegrated anode in contact with the excess of zinc remaining in the anode during the electrolysis to prevent, the going into solution of, the said -more electro-negative metal. I

6. In the electrolytlc separation of metalhc zinc-bearing materials in a number of tanks in serles circuit, the step which consists inremoving the cathode deposit including codeposited' impurities, from the first tank or tanks of the series, and commingling the cathode deposits from the later tanks ofthe series, relatively free from such impurities.

7. In the electrolytic separation of metallic zinc-bearing materials, including cadmium, in a number of tanks in series circuit, the method of recovering substantially cadmium-free cathode z1nc which consists incodepositing cadmium with the zinc in the first tank or tanks of the series, whereby the soelectrolyte which cons sts in separately treating it electrdlfittically ,to causefco-deposition' 0f the cadmium and zinc content,whereby the solution is relatively freed from cadmium, and then electrolyzing the solution in tanks of the series.

.9; In the electrolytic separation of me.

mium, in anumber of tanks in series circuit,

tallic zinc-bearing materials, including cadthe methodof recovering substantially cad- 'mium-free cathode zinc which consists in cof depositing cadmlum in a number of the first tanks of the series, the number depending upon the amount of cadmium present, Whereby the solution coming to later tanks is relatively cadmium-free and relatively purezinc is deposited in the later tanks, and segregating the deposits from the first tank or tanks and those from the later tanks. I

In testimony whereof We aflix our signatures.

CHARLES' H. ALDRICH." JOHN K. BRYAN. 

